The present invention relates to polymers, more particularly, the present invention relates to a method for removing polymeric residues and polymeric degradation products from metal surfaces, particularly metal processing equipment used in the extrusion, blending or preparation of polymeric materials. In one embodiment, the present invention relates to a composition usefully employed in cleaning such equipment of the residues remaining after blending, mixing, extruding, molding or other production operations.
It is presently known that polymeric materials may stick and melt on hot metal surfaces such as are encountered in the processing thereof. When exposed to elevated temperatures, such polymeric materials may decompose particularly when in contact with certain metals. Continued accumulation of such polymer and decomposed polymer residue may impede further production. In such case, it may be necessary to discontinue operations in order that the equipment may be thoroughly cleaned and the accumulated polymeric residue removed.
Also when changing over from one grade of polymer to another or from one pigmented polymer to a different pigmented polymer, it may be desirable to thoroughly clean the processing equipment in order to avoid contamination of the second polymer.
Periodic cleaning by mechanical means such as by wire brushing or scraping not only is time consuming and unnecessarily labor intensive but can also result in unnecessary abrasion or damage to processing equipment.
Cleaning processing equipment with chemical mixtures involves the use of purge compounds. It is known in the art that such purge compounds utilize pentaerythritol. U.S. Pat. No. 2,744,841 discloses contacting surfaces having polyethylene accumulated thereon, with pentaerythritol at a temperature above the softening point of the polyethylene. Because pentaerythritol alone does not satisfactorily clean, and in fact adheres to the processing equipment, additional steps are required for thorough cleaning. See, for example, U.S. Pat. No. 3,119,720. Thus, heretofore cleaning methods employing pentaerythritol have had to balance time and economic efficiencies with cleaning efficacy.
It would be desirable to provide an improved process for cleaning equipment employed in the preparation of polymers. In addition, it would be desirable to provide an improved process for cleaning such equipment which avoids lengthy delays and lost production. It would further be desirable to provide a method for cleaning processing equipment and purging it of accumulated polymeric residues by the use of a similar polymeric material to that which is being processed.